Do you think getting your TEFL certification is worth it?

From what I've read on this sub, I'm pretty sure what determines your chances of being accepted into JET is like 90% SOP and 10% actual qualifications/experience. But I also know that JET is very competitive, and I feel like maybe having that TEFL certification could be that little boost to my application that lets me get chosen over another applicant.

I didn't make it to the interview stage last year, so I wonder if maybe me getting my TEFL could show my initiative and how I want to improve my application from last year's? Is it common to apply without TEFL and get rejected, and then try again with your TEFL and get accepted?